@sodasix
這是我的理解，包含在外部去呼叫內部方法的實現
https://jsfiddle.net/ykx088Lv/2/

<div id="app">
    <ul>
      <li v-for="item in items">
        <span>{ item | json}</span>
        <a @click="deleteByIndex($index)">[delete it]</a>
      </li>
    </ul>
</div>

var app = new Vue({
    el: '#app',
    data: {
        items: [
            { id: 4, text: 'item one'},
            { id: 5, text: 'item two'},
            { id: 6, text: 'item three'},
            { id: 7, text: 'item four'},
        ]
    },
    methods: {
        deleteByIndex: function(index) {
            this.items.splice(index, 1)
        },
        deleteById: function(id) {
            var index = this.items.findIndex(item => item.id === id)
            this.deleteByIndex(index)
        }
  }
})

// 外部呼叫

// 刪除最後一個 (by Index
app.deleteByIndex(app.$data.items.length - 1)

// 刪除指定id ( by id
app.deleteById(4)